In one method for establishing an optical line-of-sight, a conventional method is used to form a centerline which is off-set from and parallel to the centerline of the processing machinery. Brass plugs are cemented into the floor and then prick-punched to establish reference points along the centerline. A jig transit is then aligned with the pricked-punched brass plugs and an optical line-of-sight is established at a desired distance above the centerline on the floor. Another method is disclosed in U.S. Pat. No. 4,549,360, in which a casing is permanently cemented into the floor and has means for supporting a target mount so that it may be moved in lateral directions relative to the centerline to position the centerline of a target mounted on the target mount on the centerline of the optical line-of-sight. Thereafter, the means for supporting the target mount are locked in position so that target mounts may be supported whenever desired. The target mount is then removed and a cover is provided to protect the casing and the means for supporting the target mount when not being used. Some difficulties have been encountered by persons using the method and apparatus described in U.S. Pat. No. 4,549,360 in initially positioning the means for supporting the target mounts and ensuring that such means remained in the correct position. Also, the mounting means for securing the targets on the target mounts permit deviations of the centerline of the target relative to the target mounts. Therefore, there existed a need for apparatus capable of being precisely positioned and secured so that the centerline of the target is precisely on the established optical line-of-sight centerline.